The occurrence of IgA class reticulin and endomysium antibodies was examined with the standard immunofluorescence method in coeliac disease and dermatitis herpetiformis. Similar high antibody frequencies were detected in 32 untreated adults (91%) and 18 children (100%) with coeliac disease and in 14 dermatitis herpetiformis patients with subtotal villous atrophy (reticulin antibodies 93% and endomysium antibodies 100%). The specificity of IgA class reticulin antibodies and endomysium antibodies was high because all 45 adult patients with ulcerative colitis or Crohn's disease, 24 non-coeliac children with abdominal symptoms and 99/100 healthy blood donors were negative for these antibodies. The only positive blood donor had both IgA class reticulin antibodies and endomysium antibodies but also she was found to have coeliac disease. IgA class reticulin antibodies and endomysium antibodies declined in parallel during treatment with a gluten free diet and increased on gluten challenge. This suggests that these antibodies can be used to screen for gluten sensitive enteropathy and to monitor dietary treatment. To characterise the tissue specificity of reticulin antibodies and endomysium antibodies four positive sera were absorbed with human and several rodent liver homogenates. Absorption with rat or other rodent livers removed the rodent-specific reticulin antibodies but not the reticulin antibodies detectable with human tissues or the endomysium antibodies detectable with monkey oesophagus. These results show that reticulin antibodies can be divided into the rat and human subtypes. The human subtype could not be separated from endomysium antibodies in the present absorption experiments.